1. Field of the Invention
The present invention relates to a technology for outputting image data from an image processing apparatus.
2. Description of the Related Art
Nowadays, various types of image processing apparatuses have become popular for their capability to efficiently produce a copy of image data (an electronic document or an image) by outputting the image data on a recording medium such as recording paper. During the copying operation, however, there is a risk that images not allowed to be copied or highly-confidential documents in the image data are inadvertently output. To guard against such a problem, various technologies have been disclosed that protect areas not allowed to be output (hereinafter, “output-prohibit areas”) from being inadvertently output during the copying operation.
For example, Japanese Patent Application Laid-open No. 2003-032487 discloses a technique that allows the user to set arbitrary areas on an image as output-prohibit areas not to be output at the time of copying, creates image information by appending certain patterns to the output-prohibit areas, and displays an image containing the output-prohibit areas to the user for confirmation. Moreover, Japanese Patent Application Laid-open No. 2006-094346 discloses a technique for embedding information regarding output-prohibit areas and information regarding particular patterns used to prevent copying of the output-prohibit areas in an integrated circuit (IC) tag that is attached to a printed publication such as a book and masking the patterns to protect the output-prohibit areas from being output. Furthermore, Japanese Patent Application Laid-open No. 2005-079628 discloses a technique for synthesizing tiled patterns on output-prohibit areas to protect the output-prohibit areas from being output at the time of copying. Moreover, Japanese Patent Application Laid-open No. 2007-174102 discloses a technique for printing multi-bit dot patterns (pattern codes) on an original and setting output-prohibit areas according to an information disclosure level.
In each of the abovementioned conventional techniques, when the user specifies output-prohibit areas in advance to flexibly set the security level for copying, the user-specified output-prohibit areas are subjected to masking to hide the details mentioned therein. However, by only performing masking of the output-prohibit areas, there remains a possibility that the hidden details in the output-prohibit areas are inferred to a certain extent by analogy. The situation in which such a problem may arise is when a person who has not seen data in its original form refers to the data containing masked output-prohibit areas. For example, when a person outputs data of an original stored earlier by another person or when data containing masked output-prohibit areas is distributed in a meeting, then there is a risk that the person referring to the data containing masked output-prohibit areas can infer the hidden details in the masked output-prohibit areas by analogy.
Consider a case shown in FIG. 43 in which an area of ‘new product “YYY”’ in a document ‘proposal for new products’ is specified as an output-prohibit area and therefore is masked (blacked out) to hide the details mentioned therein. As a result, a person referring to the document ‘proposal for new products’ is not able to learn about the hidden details. However, it is possible for that person to infer that there must be a new product having higher level of confidentiality than a ‘new product “XXX”’or a ‘new product “ZZZ”’ mentioned in the document. Similarly, consider a case shown in FIG. 44 in which events that occurred on August 3 are blacked out in a document ‘weekly report’. In that case, it is possible to infer by analogy that highly-confidential events must have occurred on either one or both of August 2 and August 3. Thus, as is evident from these examples, masking of output-prohibit areas is not necessarily sufficient to prevent the hidden details from being inferred by analogy.